Center strut fire protection sprinkler head

ABSTRACT

A fire protection sprinkler head having a center strut holding a valve cap closed has a pair of levers in series, fulcrumed on the center strut such that the tensile force acting on a fusible soldered joint is minimized.

[ CENTER STRUT FIRE PROTECTION 1,267,907 5/1918 R0wley 169/39 1,285,133 11/1918 Gross...... 169/39 Rowley SPRINKLER HEAD [75] Inventor:

Richard F. Juliano, Bronxville, N.Y.

The Reliable Automatic Sprinkler [73] Assignee:

Company Inc Mount Vernon, NY. Primqry ExaminerR0bert S. Ward, Jr. Jan. 31, 1972 Attorney-Granville M. Brumbaugh et a1.

[22] Filed:

Appl. No.: 221,980

ABSTRACT Int. A62c 37/12 169/37-39, 40, 42

[58] Field of Search...,.. A fire protection sprinkler head having a center strut holding a valve cap closed has a pair of levers in series,

References Cited UNITED STATES PATENTS fulcrumed on the center strut such that the tensile force acting on a fusible soldered joint is minimized.

3,161,236 Macartney............................ 169/39 11 Claims, 3 Drawing Figures PATENTEUnuv 6 ma SHEET 2 BF 2 light as possible.

CENTER STRUT FIRE PROTECTION SPRINKLER HEAD BACKGROUND OF INVENTION This invention relates to sprinkler heads, and more particularly to improved center strut fire protection sprinkler heads for automatic heat actuated fire protection systems.

For many years now, automatic fire protection sprinkler systems have employed an arrangement of struts and levers disposed between a compression screw and a valve cap which seals the sprinkler head. At some point on the strut and lever arrangement there is a fusible joint to which force is applied and which melts at the designed critical temperature to allow the strut and lever structure to collapse and allow the valve cap to open and admit water to the sprinkler head.

The principal problem relating to the sprinkler head design is to provide an arrangement of parts which is strong enough to transmit the compressive force necessary to hold the valve cap closed and, at the same time, small and light enough to require only a minimal time delay between attainment of the critical temperature in the ambient atmosphere and the collapse of the strutlever arrangement. The prior art has typically had no difficulty designing a center strut-lever arrangement which is strong enough to transmit the required compressive force, however these bulky component parts also constitute relatively massive heat sinks which must be raised by the ambient atmosphere, with its'low specific heat, to the critical temperature, before the sprinkler head can function. This insensitivity to heat is obviously a very serious problem because every second of delay in the functioning of the sprinklerhead after the critical temperature has been reached gives the fire a chance to grow and spread and makes it more difficult for the sprinkler system, when it finally does operate, to extinguish the fire. In rapidly spreading fires this problem may become a disaster if the time delay induced by the insensitivity to heat permits the fire to spread faster than the sprinkler heads can open. Therefore it is most important that the component parts of the strut and lever arrangement be made as small and I Another problem which is related to the sensitivity of the device and which the prior art has been unable to solve is the large mass and/or the large area of the fusible joint which has been necessary to resist the force applied to the joint. Typically, the prior art has had to employ either complicated arrangements which put the solder in compression or large area soldered joints in tension. The first expedient is generally unsatisfactory because it always produces cumbersome, complicated arrangements of many massive parts which are expensive to manufacture and usually require a large mass of solder with a correspondingly large heatof fusion. The resultant insensitivity to heat is obvious. The second expedient of using large area soldered joints in tension is undesirable because of high manufacturing costs, heat a, insensitivity and unaesthetic appearance. These large area joints have been necessary, however, because the lever arrangements which transmit the compressive force through the system have always produced high tensile loading on the soldered joints.

Thus, there has long existed in the art a need for areliable center strut design which uses few parts, is small 2 in mass for greater heat sensitivity, and whichproduces a small tensile force on a small soldered joint.

SUMMARY OF INVENTION Accordingly, this invention provides a novel sprinkler head which is inexpensive to manufacture, extremely sensitive to the critical temperature, highly reliable in operation, and presents a compact and aesthetically pleasing appearance.

The invention includes a center strut to which one end of a lever is secured by a soldered joint of small area. This lever is fulcrumed on a projection on the center strut, and a force is exerted on the lever by another lever which in turn is fulcrumed on the center strut adjacent the point of application of the compressive force from the compression screw. The moment arms of the levers are arranged so the force decreases from the point of application of compressive force to the soldered joint.

DESCRIPTION OF TI-IE DRAWINGS A more complete appreciation of the invention with its many attended advantages will develop as the same becomes better understood by reference to the following description of the preferred embodiment when read in conjunction with the appended drawings wherein:

FIG. 1 is an elevation, partly in section, of one embodiment of a sprinkler head according to the present invention;

FIG. 2 is an elevation taken along line 2-2 in FIG. 1; and

FIG. 3 is a cross-sectional elevation of a second embodiment of a sprinkler head according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein like or primed reference characters designate identical or corresponding parts and more particularly to FIG. 1 thereof, a sprinkler head is shown having a base 10 threaded at its lower extremity 12 for attachment to a water pipe of the sprinkler system. An axial bore 14 extends completely through base 10 and terminates in an orifice 16 through which water issues when the sprinkler functions. A cap 17 having a soft metal sealing disk 15 seats on the peripheral edges of orifice 16 to seal the bore 14. A generally oval-shaped frame 18 is connected to the base 10 and extends upwardly therefrom. An internally threaded axial bore is formed through the top of frame 18 and receives a compression screw 20, to which is attached at the top portion thereof a water deflector 22. The bottom extremity of the compression screw 20 terminates in a compression bearing 24. Compressive force is exerted on the cap 17 through a strutlever arrangement, to be described below, by applying a predetermined torque on the compression screw 20.

Referring now to FIG. 2, the strut-lever assembly includes a center strut 26 bearing, at its bottom end, against the cap 17 and, at its top end, against the under v surface of a first lever 28 at a first strut bearing point in a depression 30 provided therein for that purpose. A second depression 32 is provided on the top surface of the first lever 28 adjacent the depression 30 for receiving the compression bearing 24 of the compression screw 20. The vertically misaligned forces exerted on the first lever 28, viz, the compression force Fc exerted by the compression screw 20 and the reaction force exerted by the center strut 26, are coupled by the first moment arm a, of the first lever 28 equal to the perpendicular distance between the first strut bearing point and the line of compressive force Fc, to produce a clockwise moment M, on the first lever 28 about the first strut bearing point 30 equal to the compression force Fc multiplied by the first moment arm a,. That is:

The clockwise moment M, exerted on the first lever 28 produces a force Fl, exerted by the lower end 34 of the first lever 28 on a second lever 36 at an interlever bearing point 35. The perpendicular distance between the line of force Fl, and the first strut bearing point constitutes a second moment arm d, of the first lever about the first strut bearing point.

Since the resultant moment on the first lever 28 is zero, the force Fl, exerted by the end 34 of lever 28 is substantially equal to the compressive force Fc exerted by the compressive screw 20 multiplied by the proportion of the first moment arm a, to the second moment arm 11,. That is:

Thus the compressive force is transmitted through the center strut 26 to hold the valve cap 17 in place against the force exerted by the pressure in the sprinkler piping system and a small horizontal component is exerted by way of the first lever 28 on the second lever 36.

The long arm of the lever 28 between bearing 24 and the end 34 functions both as the long moment arm of the lever and as a shock absorbing spring. If the sprinkler head is dropped in transit, the vertical shock could damage the soft metal sealing disk or distort some of the members of the lever-strut assembly, thereby resulting in a leaky sprinkler head. To preclude this possibility, the long arm of the lever will flex resiliently when subjected to an impact deflection, thereby softly absorbing the blow and preventing damage. The long arm can also flex to accomodate changes in the vertical dimension of the frame 18 caused by temperature changes.

The second lever 36 bears at its lower end against a second strut bearing point 39 formed by a fulcrum projection 38 or the like extending from the center strut 26. Alternatively, a roller bearing lying in a shallow horizontal groove formed at the position of projection 38 could function as the fulcrum for the second lever 36. Whether or not there is an intermediate member, like the roller bearing, between the strut and the point where it contacts the levers, the levers will be referred to as fulcrumed or bearing against" the strut.

An indentation 40 is formed in the second lever 36 adjacent its point of contact with fulcrum projection 38 and receives the end 34 of the first lever 28 at the interlever bearing point 35. The indentation 40 is enlarged beyond the dimensions of the end 34 to allow some vertical adjustment in the position of the interlever bearing point 35 as compression is applied through compression screw and as dimensional changes caused by thermal expansion and contraction in the several parts occur.

The second lever 36 is bent at a right angle 41 and extends through an opening 42 in the center strut 26. The top end of the second lever 36 is secured to the center strut 26 by a fusible connection means comprising a small plate 44 which is soldered to the center strut 26. The second lever 36 is linked to the plate 44 by passing the end 45 of the second lever 36 under a bail 46 which extends out from the plate 44. The bail 46 is preferably formed by a stamping operation and is located centroidally on the plate 44.

The force Fl, exerted by the end 34 of the first lever 28 on the second lever 36 and the reaction force exerted on the second lever by the fulcrum projection 38 at the second strut bearing point 39 are coupled by the first moment arm a which is the perpenciular distance between the line of force F1, and the second strut bearing point 39, to produce a counterclockwise moment M about the second strut bearing point 39. This moment is equal to the first moment arm a, of the second lever 36 multiplied by the force Fl, exerted by by the first lever 28. This moment is counteracted by a clockwise moment exerted on the lever 36 equal to the resisting force F1 exerted by the bail 46 on the upper end of the lever 36 multiplied by the second moment arm of the second lever, which is the perpendicular distance (1 between the line of force of Fl and the second strut bearing point. Since these moments balance,

F1 a ld Fl,

and since, as previously indicated,

Fl, a,/d, Fc

therefore Fl a,/d 'a /d Fc Thus the tensile force exerted on the solder joint is greatly reduced to the point where a solder joint of small area is feasible.

Looking now at FIG. 3, a second embodiment of the double lever-center strut system is shown using the same base 10, frame 18, compression screw 20 and deflector 22 as was used in the first embodiment of FIGS. 1 and 2. A center strut 26' bears at its lower end against the valve cap 17 and transmits compressive force from the compression screw 20 to hold the valve cap 17 in place. The center strut 26' bears at its upper end against a first lever 28' at a first strut bearing point in a depression 30 provided in the under surface thereof for that purpose. A second depression 32' is provided in the upper surface of the first lever 28 for receiving the compression bearing 24 of the compression screw 20 at a compression screw bearing point. The unbalanced forces, Fc exerted by the compression screw 20, and the reaction force exerted by the center strut 26' are coupled by a first moment arm a, of the first lever to produce a counter-clockwise moment M, on the first lever 28' equal to the compressive force Fc multiplied by the moment arm a, which is equal to the perpendicular distance between the line of force Fc of compression screw 20 and the first strut bearing point.

This counterclockwise moment is resisted by a force Fl, exerted by a bearing projection 34' on the lower end of the first lever 28' at an interlever bearing point 35'. The clockwise moment, equal and opposite to the counterclockwise moment, is equal to the force Fl, multiplied by the moment arm d, which is the perpendicular distance between the line of force F1, and the first strut bearing point. Thus:

Fc a, Fl, d,

and

F1 a,'/d," Fe

The bearing projection 34' bears against the lower end of a second lever 36 which, in turn, extends through an opening 42' in the center strut 26' and bears against a second strut bearing point 39 at a fulcrum projection 38' formed on the center strut 26' at a perpendicular distance a, above the line of force Fl, constituting a first moment arm of the second lever 36' The top of the second lever 36 is secured to the center strut 26 by means of a fusible connection means comprising a small plate 44' soldered to center strut 26'. A bail 46' is formed centroidally on the plate 44' and the upper end of the second lever 36 is hooked under the bail 46' to link-second lever 36' to the plate 44'. The perpendicular distance between the line of the force F1 exerted by the bail 46' on the upper end of the lever 36, and the second strut bearing point 39' constitutes the second moment arm d of the second lever 36'.

The counterclockwise moment on the second lever 36' about the second strut bearing point 39' is equal to the force Fl, exerted thereon by the first lever 28" multiplied by the first moment arm a, and this moment is counteracted by the equal and opposite clockwise moment about the second strut bearing point 39' equal to the force Fl exerted by the bail 46 of the plate 44( on the upper end of the second lever 36' multiplied by the second moment arm d That is F11. a2 Flg d2 and Fl a 'ld Fl,

Therefore 7 j 2 n e Thus the tensile force exerted on the soldered joint may be held to afsmall magnitude to permit the use of a soldered joint of small area.

It is now clear that, by the use of this unique double lever-center strut arrangement, it is possible to design the various moment arms in such' a way as to permit the use of very few, light weight parts and a soldered area in tension which is much smaller than that achieved by the prior art. This design makes possible a significant improvement in the heat sensitivity of the device while at the same time reducing the manufacturing'costs and providing a sprinkler head of pleasing aesthetic appearance.

Obviously numerous modifications and variations of the preferred embodiment disclosed herein are possible in light of this disclosure. Therefore it is expressly to be understood that the invention may be practiced otherwise than as specifically disclosed herein while remainadjustable compression screw, wherein the improve ment comprises:

a lever system connected in series between said compression screw and a fusible connection with said center strut, said lever system including two levers fulcrumed on said center strut at a point nearer one end of each lever than the other end, the longer portion of each lever extending in the direction in which force is transmitted from the compression screw to thefusible connection, said levers and center strut forming a lever-strut arrangement disposed to progressively reduce the force applied through said lever system from said compression screw to said fusible connection, said fusible connection preventing the lever-strut arrangement from collapsing under the compressive force exerted by said compression screw until said fusible connection fuses.

2. A fire protection sprinkler as defined in claim 1,

wherein:

the longer portion of each of said levers constitutes a long moment arm, and the shorter portion of each of said levers constitutes a short moment arm about the respective point at which the respective lever is fulcrumed on said center strut; the end of the short moment arm of the first of said levers bears against said compression screw, and the end of the long moment arm of said first lever bears against the end of the short moment arm of the second of said levers; and the end of the-long moment arm of the second of said levers bears against said fusible connection with said center strut. 3. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and seal- I ing said bore, and a frame connected to said body and ing within the spirit and scope of the appended claims. I

I claim:

1. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, a center strut bearing against said valve, and a frame connected to said body and mounting an mounting an adjustable compression screw, wherein the improvement comprises:

a center strut vertically misaligned with said compression screw and bearing at one end against said valve;

first coupling means between said center strut and said compression screw for converting a portion of the compressive force'froms aid compression screw to a first moment;

first moment arm means, longer than said first coupling means, for converting said first moment to a second force of substantially less magnitude than said compressive force;

secondcoupling means between the end of said first moment arm means and said center strut for converting said second force to a second moment;

second moment arm means, longer than said second coupling means, for converting said second moment to a third force of substantially less magnitude than said second force; and

fusible means fusibly connecting the end of said second moment arm means to said center strut for resisting said third force until fusion of said fusible means.

4. A fire protection sprinkler as defined in claim 3,

wherein:

said first coupling means and said first moment arm means are embodied in a first lever bearing at the end of said first moment arm means against a second lever; and said second lever embodies said second coupling means and said second moment arm.

5. A fire protection sprinkler as defined in claim 4, wherein:

said fusible means comprises a small plate soldered to said center strut and linked, at a connection point disposed centrally thereon, to said second lever.

6. A fire protection sprinkler having a body, a bore through said body, a valve adapted to seat on said body to seal said bore, a center strut bearing at one end against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises:

a series of at least two levers each fulcrumed on said center strut and each having a long and a short moment arm about their respective fulcrum point;

the first of said levers bearing at the end of the short moment arm thereof against said compression screw, and bearing at the end of the long moment arm thereof against the second of said levers;

the second of said levers bearing at the end of the short moment arm thereof against said first of said levers, and being secured against movement by fusible connection means at the end of the long moment arm of said second lever.

7. A fire protection sprinkler as defined in claim 6,

wherein:

said fusible connection means comprises a small plate soldered to said center strut and linked, at a centrally disposed point of connection on said plate to said second lever.

8. A fire protection sprinkler having a body, a bore through said body, a valve adapted to seat on said body to seal said bore, a center strut bearing at one end thereof against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises:

a first lever, bearing adjacent one end thereof against said strut at a first strut bearing point;

said compression screw bearing against said first lever adjacent said first strut bearing point;

a second lever having one end secured against movement by fusible connecting means;

said second lever bearing against said center strut at a second strut bearing point;

the other end of said first lever bearing against said second lever at an interlever bearing point;

the perpendicular distance between said first strut bearing point and the line of force exerted by said compression screw constituting a first moment arm of said first lever;

the perpendicular distance between said first strut bearing point and the line of force exerted between said first and second levers at said interlever bearing point constituting a second moment arm of said first lever;

said second moment arm of said first lever being longer than said first moment arm of said first lever;

the perpendicular distance between the line of force exerted between said first and said second levers at said interlever bearing point and said second strut bearing point constituting a first moment arm of said second lever;

the perpendicular distance between the line of force exerted between said fusible connection means and said second lever, and said second strut bearing point constituting a second moment arm of said second lever;

said second moment arm of said second lever being longer than said first moment arm of said second lever.

9. A fire protection sprinkler as defined in claim 8,

wherein:

said fusible connecting means comprises a small plate soldered to said center strut and linked at a centrally disposed point of connection on said plate to said second lever.

10. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, a center strut bearing against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises:

a lever system connected in series between said compression screw and a fusible connection with said center strut;

said lever system including two levers fulcrumed on said center strut;

each of said levers having a long moment arm and a short moment arm about the respective point at which the respective lever is fulcrumed on said center strut;

the first of said levers bearing at the end of the short moment arm thereof against said compression screw, and bearing at the end of the long moment arm of said first lever against the end of the short moment arm of the second of said levers;

said second of said levers bearing at the end of the long moment arm thereof against said fusible connection with said center strut;

said levers forming with said center strut a lever-strut arrangement disposed to progressively reduce the force applied through said lever system from said compression screw to said fusible connection means, said fusible connection means preventing the lever-strut arrangement from collapsing under the compressive force exerted by said compression screw until said fusible connection fuses.

11. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises:

a center strut vertically misaligned with said compression screw and bearing at one end against said valve;

a first lever including first coupling means between said center strut and said compression screw for converting a portion of the compressive force from said compression screw to a first moment, and first moment arm means for converting said first moment to a second force of substantially less magnitude than said compressive force;

a second lever including second coupling means bev tween the end of said first moment arm means and said center strut for converting said second force to a second moment, and second moment arm means for converting said second moment to a third force of substantially less magnitude than said second force;

said first lever bearing, at the end of said first moment arm means, against said second lever; and

fusible means comprising a small plate soldered to said center strut and linked at a connection point disposed centrally thereon to said second lever for connecting the end of said second moment arm means to said center strut for resisting said third force until fusion of said fusible means.

K l *l 

1. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, a center strut bearing against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a lever system connected in series between said compression screw and a fusible connection with said center strut, said lever system including two levers fulcrumed on said center strut at a point nearer one end of each lever than the other end, the longer portion of each lever extending in the direction in which force is transmitted from the compression screw to the fusible connection, said levers and center strut forming a lever-strut arrangement disposed to progressively reduce the force applied through said lever system from said compression screw to said fusible connection, said fusible connection preventing the lever-strut arrangement from collapsing under the compressive force exerted by said compression screw until said fusible connection fuses.
 2. A fire protection sprinkler as defined in claim 1, wherein: the longer portion of each of said levers constitutes a long moment arm, and the shorter portion of each of said levers constitutes a short moment arm about the respective point at which the respective lever is fulcrumed on said center strut; the end of the short moment arm of the first of said levers bears against said compression screw, and the end of the long moment arm of said first lever bears against the end of the short moment arm of the second of said levers; and the end of the long moment arm of the second of said levers bears against said fusible connection with said center strut.
 3. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a center strut vertically misaligned with said compression screw and bearing at one end against said valve; first coupling means between said center strut and said compression screw for converting a portion of the compressive force from said compression screw to a first moment; first moment arm means, longer than said first coupling means, for converting said first moment to a second force of substantially less magnitude than said compressive force; second coupling means between the end of said first moment arm means and said center strut for converting said second force to a second momEnt; second moment arm means, longer than said second coupling means, for converting said second moment to a third force of substantially less magnitude than said second force; and fusible means fusibly connecting the end of said second moment arm means to said center strut for resisting said third force until fusion of said fusible means.
 4. A fire protection sprinkler as defined in claim 3, wherein: said first coupling means and said first moment arm means are embodied in a first lever bearing at the end of said first moment arm means against a second lever; and said second lever embodies said second coupling means and said second moment arm.
 5. A fire protection sprinkler as defined in claim 4, wherein: said fusible means comprises a small plate soldered to said center strut and linked, at a connection point disposed centrally thereon, to said second lever.
 6. A fire protection sprinkler having a body, a bore through said body, a valve adapted to seat on said body to seal said bore, a center strut bearing at one end against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a series of at least two levers each fulcrumed on said center strut and each having a long and a short moment arm about their respective fulcrum point; the first of said levers bearing at the end of the short moment arm thereof against said compression screw, and bearing at the end of the long moment arm thereof against the second of said levers; the second of said levers bearing at the end of the short moment arm thereof against said first of said levers, and being secured against movement by fusible connection means at the end of the long moment arm of said second lever.
 7. A fire protection sprinkler as defined in claim 6, wherein: said fusible connection means comprises a small plate soldered to said center strut and linked, at a centrally disposed point of connection on said plate to said second lever.
 8. A fire protection sprinkler having a body, a bore through said body, a valve adapted to seat on said body to seal said bore, a center strut bearing at one end thereof against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a first lever, bearing adjacent one end thereof against said strut at a first strut bearing point; said compression screw bearing against said first lever adjacent said first strut bearing point; a second lever having one end secured against movement by fusible connecting means; said second lever bearing against said center strut at a second strut bearing point; the other end of said first lever bearing against said second lever at an interlever bearing point; the perpendicular distance between said first strut bearing point and the line of force exerted by said compression screw constituting a first moment arm of said first lever; the perpendicular distance between said first strut bearing point and the line of force exerted between said first and second levers at said interlever bearing point constituting a second moment arm of said first lever; said second moment arm of said first lever being longer than said first moment arm of said first lever; the perpendicular distance between the line of force exerted between said first and said second levers at said interlever bearing point and said second strut bearing point constituting a first moment arm of said second lever; the perpendicular distance between the line of force exerted between said fusible connection means and said second lever, and said second strut bearing point constituting a second moment arm of said second lever; said second moment arm of said second lever being longer than said first moment arm of said second lever.
 9. A fire protection sprinkler as defined in claim 8, wherein: said fusible connecting means comprises a small plate soLdered to said center strut and linked at a centrally disposed point of connection on said plate to said second lever.
 10. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, a center strut bearing against said valve, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a lever system connected in series between said compression screw and a fusible connection with said center strut; said lever system including two levers fulcrumed on said center strut; each of said levers having a long moment arm and a short moment arm about the respective point at which the respective lever is fulcrumed on said center strut; the first of said levers bearing at the end of the short moment arm thereof against said compression screw, and bearing at the end of the long moment arm of said first lever against the end of the short moment arm of the second of said levers; said second of said levers bearing at the end of the long moment arm thereof against said fusible connection with said center strut; said levers forming with said center strut a lever-strut arrangement disposed to progressively reduce the force applied through said lever system from said compression screw to said fusible connection means, said fusible connection means preventing the lever-strut arrangement from collapsing under the compressive force exerted by said compression screw until said fusible connection fuses.
 11. A fire protection sprinkler having a body, a bore through said body, a valve seated on said body and sealing said bore, and a frame connected to said body and mounting an adjustable compression screw, wherein the improvement comprises: a center strut vertically misaligned with said compression screw and bearing at one end against said valve; a first lever including first coupling means between said center strut and said compression screw for converting a portion of the compressive force from said compression screw to a first moment, and first moment arm means for converting said first moment to a second force of substantially less magnitude than said compressive force; a second lever including second coupling means between the end of said first moment arm means and said center strut for converting said second force to a second moment, and second moment arm means for converting said second moment to a third force of substantially less magnitude than said second force; said first lever bearing, at the end of said first moment arm means, against said second lever; and fusible means comprising a small plate soldered to said center strut and linked at a connection point disposed centrally thereon to said second lever for connecting the end of said second moment arm means to said center strut for resisting said third force until fusion of said fusible means. 